1. [Field of the Invention]
The present invention relates to a magnetic detector for detecting a magnetic field and, more specifically, to a magnetic apparatus for detecting changes in magnetic field caused by the rotation of a magnetic material or the like and to a production process therefor.
2. [Description of the Prior Art]
FIGS. 8(a) and 8(b) are structural diagrams of a magnetic detector of the prior art, FIG. 8(a) is a top view and FIG. 8(b) is a sectional view taken on line A--A of FIG. 8(a). This magnetic detector comprises a magnetic resistance element for detecting a magnetic field (to be referred to as "MR element" hereinafter), a magnet 2 for providing a bias magnetic field to the MR element 1, a protection circuit 4 composed of a plurality of electronic parts 3 for removing external noise from the output waveform of the MR element 1, a lead frame 5 for mounting the electronic parts 3, a base 6 for holding the MR element 1, the magnet 2 and the lead frame 5, a case 7 for protecting the base 6, and a connector 8, integrated with the base 6, for outputting the output signal of the MR element 1 to the outside.
The base 6 is insert molded together with the magnet 2 after the electronic parts 3 forming the protection circuit 4 are mounted on the lead frame 5, and the MR element 1 is soldered to an element attachment portion 5k of the lead frame 5 exposed on the base 6 integrated with the connector 8 after the formation of the base 6.
After the attachment of the MR element 1, the base 6 is press fitted in a press-in hole 7k of the case 7 and fixed at a press-in portion 6k formed at an upper portion (left side of FIG. 8(b)) of the base 6. Liquid packing P is coated on the outer periphery of the press-in portion 6k to cover up tight an inside portion 7s of the case 7. Further, to fix the base 6 to the case 7 firmly, an upper portion of the case 7 is filled with a thermosetting resin adhesive 9 (shown by slant lines of FIG. 8(b)).
As shown in FIG. 9, the MR element 1 has a thin film magnetic resistance pattern 1b made from a magnetic material having a large magnetic resistance effect, such as permalloy, formed on the substrate 1a made from ceramic or the like. The resistance value of the magnetic resistance pattern 1b changes according to the size of a magnetic field applied to the magnetic resistance pattern 1b. Then, the MR element 1 is arranged next to a magnetic rotor 50 having an irregular surface on the outer periphery and rotating around a rotation axis J with predetermined spacing therebetween to detect changes in the strength of a magnetic field it receives from the magnetic rotor 50, whereby the rotation position or rotation speed of the magnetic rotor 50 can be obtained.
However, in the above magnetic detector of the prior art, since the connector 8 and the base 6 are integrated with each other, the shape of the magnetic detector is complex and the production cost of a mold used to produce the magnetic detector is high. In addition, when the shape of the connector 8 or the position of the connector 8 with respect to the case 7 is changed, a mold for producing the base 6 and the connector 8 integrally must be newly fabricated, thereby further boosting equipment costs.
When the base 6 is to be press fitted in the case 7, since the inside of the case 7 is empty and the base 6 is covered up tight in the case 7, the liquid packing P must be coated on the outer periphery of the press-in portion 6k to protect the MR element 1 in the case from moisture, dust and the like. Thereby, productivity deteriorates and costs rise.
Further, when the thermosetting resin adhesive 9 is to be injected into the upper portion of the case 7, the resin adhesive 9 often overflows from the case 7 and adheres to the side surface of the case 7. Therefore, a checking step must be provided to remove the adhered resin adhesive 9, thereby boosting the production cost.
To improve the characteristic properties of the magnetic detector, the MR element 1 must be arranged in front of the magnet 2. However, as the MR element 1 and the base for holding the magnet 2 are produced as separate units, the MR element 1 must be soldered to the lead frame 5 exposed on the base 6 while it is located at a predetermined position in front of the magnet 2, thereby reducing productivity and boosting costs.
Moreover, as shown in FIGS. 10(a) and 10(b), solder S for mounting electronic parts 3 (shown by slant lines in FIG. 10(b) previously coated on a land portion 5a of the lead frame 5 may flow away at the time of soldering the electronic parts 3, thereby reducing the reliability of the apparatus. For comparison, the shape of the lead frame 5 of FIGS. 10(a) and 10(b) is made similar to that of the lead frame of the present invention which will be described hereinafter.